In a small bowl, combine cracker crumbs and sugar; stir in butter. Press onto the bottom of a 13-in. x 9-in. baking dish coated with cooking spray. Cover and refrigerate for at least 15 minutes.
In a large bowl, beat cream cheeses and sugar until smooth. Beat in the pumpkin, flour, pie spice and vanilla. Add eggs; beat on low speed just until combined. Pour over crust.
Bake at 325° for 35-45 minutes or until center is almost set. Cool on a wire rack for 1 hour. Cover and refrigerate for 8 hours or overnight.
Cut cheesecake into 20 bars; top each with a walnut half.
Yield: 20 bars